Eustatic and regional tectonic controls on late Pleistocene paleovalley morphology in the central Kanto Plain, Japan.

This study analyzed the morphology of three late Pleistocene buried paleovalleys in the central Kanto Plain, Japan, by using data from sedimentary cores and boreholes. The paleo-Arakawa valley and the paleo-Nakagawa valley merge to form the paleo-Tokyo valley, which extends into Tokyo Bay. Although the last glacial sea-level fall controlled the formation of these paleovalleys, fluvial terraces developed differently in these paleovalleys, reflecting regional differences in tectonic activity. The paleo-Tokyo valley beneath the Tokyo Lowland, and the paleo-Arakawa valley beneath the Arakawa Lowland, are in relatively stable or uplifting regions, and both paleovalleys have several distinct fluvial terraces forming stepped cross-sectional profiles. In contrast, in the paleo-Nakagawa and the paleo-Arakawa valleys beneath the subsiding Menuma Lowland, terrace surfaces are obscure and there is a smooth gradient from the valley margins to the valley axis. The structure of the paleovalleys in the central Kanto Plain can thus be explained by the combination of eustatic sea-level fall and concurrent regional tectonic movement. [ABSTRACT FROM AUTHOR]